LONDON — Almost a third of the world is now fat, and no country has been able to curb obesity rates in the past three decades, according to a new global analysis.

Researchers found more than 2 billion people worldwide are now overweight or obese. The highest rates were in the Middle East and North Africa, where nearly 60 percent of men and 65 percent of women are heavy. The U.S. has about 13 percent of the world's fat population, a greater percentage than any other country. China and India combined have about 15 percent.

"It's pretty grim," said Christopher Murray of the Institute for Health Metrics and Evaluation at the University of Washington, who led the study. He and colleagues reviewed more than 1,700 studies covering 188 countries from 1980 to 2013. "When we realized that not a single country has had a significant decline in obesity, that tells you how hard a challenge this is."

Murray said there was a strong link between income and obesity; in developing countries, as people get richer, their waistlines also tend to start bulging. In many rich countries like the U.S. and Britain, the trend is reversed — though only slightly. Murray said scientists have noticed accompanying spikes in diabetes as obesity has risen and that rates of cancers linked to weight, like pancreatic cancer, are also rising.

The new report was paid for by the Bill & Melinda Gates Foundation and published online Thursday in the journal Lancet.